The present invention generally relates to electric motors/generators and electrically driven compressors and, more particularly, to a cooling jacket resistor of a refrigerant-vapor cooled electric motor/generator and a method for draining condensed refrigerant from a cooling jacket.
An electric motor converts electrical energy into kinetic energy, whereas the reverse task, that of converting kinetic energy into electrical energy, is accomplished by a generator. A typical electric motor consists of an outside stationary stator producing a rotating magnetic field and an inside rotor attached to the output shaft that is given a torque by the rotating field. Generally, a considerable amount of heat is generated during the operation of the electric motor and it may be desirable to cool the space between the rotor shaft and the stator as well as the motor stator, especially when the motor is operated at high speeds.
In the past, various cooling structures for cooling an electric motor have been developed, such as providing passages for a coolant at the circumference of a motor or a cooling jacket for circulating a coolant fluid in grooves around the stator. It is also known in the art, that the motor of an electrically driven compressor may be cooled by liquid refrigerant, by refrigerant vapor, or a combination thereof.
U.S. Pat. No. 4,903,497, for example, teaches grooves between a stator and a motor housing for circulation of a liquid refrigerant that is in an at least partly vapor state, and which cools the stator without any short-circuit in the stator coils.
U.S. Pat. No. 3,218,825, for example, teaches conducting liquid refrigerant through passageways of the motor stator to cool the stator by evaporation of the refrigerant and conducting the vaporized refrigerant to a condenser or an evaporator.
Furthermore, U.S. Pat. No. 6,997,686 teaches a cooling jacket mounted around a stator of an electric motor, which drives a two-stage compressor. A liquid refrigerant passes through corkscrew-shaped grooves on the circumference of the cooling jacket from an inlet to an outlet, thereby cooling the motor stator. Additionally, refrigerant gas may pass through a gap between the motor rotor and stator. The gas may serve to remove heat from the motor rotor and bearings. The gas may be propelled through the compressor by the pressure differential between the first and second stages. The gas may flow from the second impeller through several bearings and spaces between the motor rotor and the stator and may empty out into the discharged gas from the first impeller.
While circulating a refrigerant gas through gaps between the motor rotor and stator may supplement the cooling of the rotor with a liquid refrigerant, problems may arise when the operation of the motor is stopped. Refrigerant gas trapped within the gaps between the rotor and the stator may condense and, consequently, become liquefied. This condensed liquid may be trapped inside a cooling jacket and may become a problem if accumulated. Prior art outlets for the refrigerant gas used for cooling the rotor/stator may not be suitable for draining the condensed refrigerant. Liquid trapped inside the cooling jacket may cause damage on part of the motor, such as bearings and electrical connections. If a refrigerant gas, especially a refrigerant with a relatively high conductivity, is used inside a cooling jacket, it may require special insulation of electric wires of the motor.
As can be seen, there is a need for a mechanism that allows draining the condensed refrigerant from a cooling jacket of an electric motor where the internal space of a cooling jacket is cooled with a refrigerant gas. Furthermore, there is a need for a method of draining condensed liquid refrigerant from the internal space of a cooling jacket that does not impair the primary stator/rotor cooling scheme.